The problem of school readiness is significant. The most recent results of the National Association of Educational Progress indicate that among 4th grade children in the United States only 31% perform at or above proficient levels in reading and math. In both domains, children from lower SES backgrounds performed significantly below the levels of achievement attained by children from higher SES backgrounds, indicating that the effects of poverty on the development of children's skills evident in preschool are persistent. The primary aims of this randomized intervention study are to determine if (a) a high quality school readiness curriculum will significantly and substantially increase the later academic performance of 4- year-old children who are at risk of academic difficulties because of conditions associated with living in poverty, (b) substantial differences in children's socio-emotional development are obtained depending on whether the curriculum includes an explicit curriculum component designed to promote socio-emotional skills versus an implicit socio-emotional curriculum achieved by high quality professional development, and (c) curriculum-linked assessment promotes greater teacher scaffolding of children's school readiness skills compared to progress monitoring assessment. Using block-randomization, 100 classrooms in two waves of 50 classes in Tallahassee, FL and Houston, TX will be assigned to 5 treatment conditions: (a) "business as usual" control classes, (b) explicit socio-emotional curriculum with progress monitoring assessment, (c) explicit socio-emotional curriculum with curriculum-linked assessment, (d) implicit socio-emotional curriculum with progress monitoring assessment, and (e) implicit socio-emotional curriculum with curriculum-linked assessment. Multi-level hierarchical linear modeling will examine effects of curriculum variations for 8 children from each class (N = 800 total) who will be randomly selected for assessments to be conducted at the start, middle, and end of the preschool year, as well as at the end of kindergarten and first grade.